What is the tensile strength of elastomers?
The tensile strength is the tensile stress that is applied to an elastomeric specimen during the tensile test at the moment of rupture. It is calculated from the force during the tensile test and the initial cross-sectional area and is expressed in N/mm² or MPa. For most cross-linked elastomers, the tensile strength is equal to the tensile strength. The English term is „tensile strength at break“.
| Characteristic | Indication |
|---|---|
| Key value | Tensile strength (English: tensile strength at break) |
| Formula symbols | σR |
| Unity | N/mm² or MPa (1 N/mm² = 1 MPa) |
| Definition | Force at the moment of tearing, based on the initial cross-section |
| Testing standards | DIN 53504:2017-03, ISO 37:2024 |
| Typical sample body | Shoulder bar S2 according to DIN 53504 |
| Test temperature | 23 °C |
| Value range of technical elastomers | about 4 to 50 MPa |
How is tensile strength calculated?
The tensile strength is calculated from the force at the moment of tearing and the initial cross-section of the test specimen.
From the Force FR (in N), where the test specimen tears, and its initial cross-section A0 (in mm²) the tensile strength results σR (in N/mm²).
Computational example: A test specimen with a width of 4 mm and a thickness of 2 mm has an initial cross-sectional area of 8 mm². If the test specimen is torn at a force of 96 N, the tensile strength is
The tensile strength is always taken as the cross-sectional area before the test begins. Because an elastomer becomes significantly thinner under stretching, the actual strain in the material during tearing is many times higher than the calculated tensile strength. This actual strain is referred to as the „true strain“.
What tensile strength do elastomers have?
Polyurethane, HNBR and natural rubber have the highest tear strengths among elastomers, while silicone rubber has the lowest. The recommended values for tear strength apply to common industrial blends containing fillers at room temperature.
| Elastomer | Abbreviations | Tensile strength in MPa |
|---|---|---|
| Polyurethane | AU, EU | 20–50 |
| Hydrated nitrile rubber | HNBR | 15–35 |
| Natural rubber | NR | 15–30 |
| Nitrile rubber | NBR | 10–25 |
| Fluoroplastic | FKM | 8–20 |
| Ethylene-propylene-diene rubber | EPDM | 7–20 |
| Silicone rubber | VMQ | 4–11 |
What is the difference between tear strength and tensile strength?
Toughness and Tensile strength They are determined in the same tensile test. Tensile strength refers to the highest force in the test; tensile strength refers to the force at the moment of tearing. In most cross-linked elastomers, the force increases until tearing occurs. The highest force is therefore the tearing force; tensile strength and tensile strength are the same. In hard thermoplastic elastomers, the specimen before tearing: it begins to flow and can be further stretched at lower forces until it tears. The highest force is then present before tearing, and the tensile strength is greater than the tensile strength. The tensile strength is therefore always equal to or greater than the tensile strength.
Is the tear strength the same as the tear resistance?
No. The tensile strength indicates the tension at which an intact test specimen tears during the tensile test and is expressed in MPa. The ultimate tensile strength, also called the ultimate tear strength, indicates the force required to tear a pre-existing tear further. It is measured on a pre-cut specimen and is expressed in N/mm. Both values are not directly related. The stress is concentrated at the tip of a crack, so an uncut elastomer specimen fails at significantly lower loads than an intact one. It is therefore possible that an elastomer with high tensile strength can also have a low ultimate tear strength.
